1) Sientifid / Atlantis (Comcast is IPS)
2) Linksys 10/100 5-port workgroup switch
3) 3 computers / 1 X-Box
4) HUH???
You got a switch, not a router. It is not providing DHCP to your PC's. Which cable company are you dealing with? If it is one of those companies that only provides you one ethernet address, then this setup won't work for more than one computer at a time.
In answering question #2 could you be a little more specific. Do you still have the box it came in ? A very popular Linksys router model would be the WRT-54G. Is there anything resembling that kind of designation on the router or it’s box ?
2) Linksys 10/100 5-port workgroup switch
A "switch" is also sometimes called a "hub" which is a "dumb" device that connects computers and other network devices together. A "router" is an intelligent device that can also act as a firewall, which protects your home network.
If you have a switch, depending on your Internet service, only 1 computer will have the ability to get on the Internet, and it will be completely exposed to the Internet. SO TURN OFF YOUR COMPUTERS RIGHT NOW!This assumes that you only get a single IP address from your ISP. What you need is to buy a router, like a Linksys, SMC, Netgear, or any of a number of others. But don't throw away your Linksys Switch... Most routers have a 4 port switch built in, but if you need more than just 4 ports, you can "daisy chain" your 5 port linksys switch to the router you're going to buy. That will give you 7 usable ports. On the other hand, if you won't be needing more than 4 ports, you might be able to return the linsys switch for a refund.
But what you definitely need is a router.
Mark